TGF-β denotes a family of proteins, TGF-β1, TGF-β2 and TGF-β3, which are pleiotropic modulators of cell proliferation and differentiation, wound healing, extracellular matrix production and immunosuppression. Other members of this superfamily include activins, inhibins, bone morphogenetic proteins, growth and differentiation factors and Müllerian inhibiting substance.
TGF-β1 transduces signals through two highly conserved single transmembrane serine/threonine kinases, the type I (ALK5) and type II TGF-β receptors. Upon ligand induced oligomerization, the type II receptor hyperphosphorylates serine/threonine residues in the GS region of the ALK5, which leads to activation of the ALK5 by creating a binding site for Smad proteins. The activated ALK5 in turn phosphorylates Smad2 and Smad3 proteins at the C-terminal SSXS-motif thereby causing their dissociation from the receptor and heteromeric complex formation with Smad4. Smad complexes translocate to the nucleus, assemble with specific DNA-binding co-factors and co-modulators to finally activate transcription of extracellular matrix components and inhibitors of matrix-degrading proteases.
Activins transduce signals in a manner similar to TGF-β. Activins bind to serine/thereonine kinase, the activin type II receptor (ActRIIB), and the activated type II receptor hyperphosphorylates serine/threonine residues in the GS region of the ALK4. The activated ALK4 in turn phosphorylates Smad2 and Smad3. The consequent formation of a hetero-Smad complex with Smad4 results in the activin-induced regulation of gene transcription.
Numerous experimental animal studies demonstrate an association between glomerular expression of TGF-β and fibrosis, including the Thy-1 rat model of proliferative glomerulonephritis, anti-GBM glomerulonephritis in rabbits, and the 5/6 nephrectomy rat model of focal segmental glomerulosclerosis, as has been reviewed recently (e.g., Bitzer, M. et al., Kidney Blood Press. Res. 21:1-12 (1998)). Neutralizing antibody to TGF-β improves glomerular histology in the Thy-1 nephritis model (e.g., Border, W. A. et al., Nature 346: 371-374 (1990)).
Hyperglycemic conditions increase TGF-β mRNA and protein synthesis in both murine proximal tubule cells and human mesangial cells (e.g., Wahab, N. A. et al., Biochem. J. 316:985-992 (1996); Rocco, M. V. et al., Kidney Int. 41: 107-114 (1992)). Diabetic patients with early kidney disease show increased accumulation of TGF-β mRNA and protein within the glomerulus (e.g., Yoshioka, K. et al., Lab. Invest. 68: 154-163 (1993)). In kidneys with chronic renal interstitial fibrosis, the hallmarks are thickened tubular basement membranes and an expanded interstitial compartment, with interstitial fibrosis characterized by an increase in collagens I, III, V, VII, and fibronectin (e.g., Eddy, A. A., J. Am. Soc. Nephrol. 7: 2495-2508 (1996)).
TGF-β gene expression and protein production are increased in a variety of animal models of pulmonary fibrosis including bleomycin, silica, asbestos, and radiation (e.g., Phan, S. H. and Kunkel, S. L., Exp. Lung Res. 18: 29-43 (1992); Williams, A. O. et al., Am. J. Pathol. 142: 1831-1840 (1993); Rube, C. E. et al., Int. J. Radiat. Oncol. Biol. Phys. 47: 1033-1042 (2000)). Coincident increase in TGF-β1 protein and collagen gene expression in adjacent tissue slices from idiopathic pulmonary fibrosis is observed in human pulmonary fibrotic disease (e.g., Broekelmann, T. J. et al., Proc. Natl. Acad. Sci. USA 88:6642-646 (1991)). Increased TGF-β production has been documented in patients with sarcoidosis, pneumoconiosis, asbestosis, and radiation-induced fibrosis (e.g., Khalil, N. et al., Am. J. Respir. Cell. Mol. Biol. 14:131-138 (1996); Jagirdar, J. et al., Environ. Health Perspect. 105:1197-1203 (1997)). Anti-TGF-β antibodies and TGF-β-soluble receptors could partially inhibit fibrosis in bleomycin-induced lung fibrosis rodent models (e.g., Giri, S. N. et al., Thorax 48: 959-966 (1993); Wang, Q. et al., Thorax 54: 805-812 (1999)). Tobacco smoke has been implicated as one of the most important factors that can cause small airway disease followed by chronic obstructive pulmonary disease (COPD) (e.g., Wright, J. M. et al., Am. Rev. Respir. Dis. 146: 240-262 (1992)). COPD is a slowly progressive and irreversible disorder characterized by the functional abnormality of airway obstruction. TGF-β has been hypothesized to be involved in airway remodeling found in chronic airway inflammatory disorders such as COPD (e.g., Takizawa, H. Int. J. Mol. Med. 1: 367-378 (1998); Ning, W. et al., Proc. Natl. Acad. Sci. USA 101:14895-14900 (2004)).
Hepatic stellate cells (HSC) are the major source of extracellular matrix proteins in hepatic fibrosis. Extracellular matrix production by activated hepatic stellate cells is markedly increased through the action of TGF-β1 (e.g., Friedman, S. L., Prog. Liver Dis. 14: 101-130 (1996); Pietrangelo, A., Semin. Liver Dis. 16:13-30 (1996)). Transgenic mice that overexpress TGF-β1 in the liver develop hepatic fibrosis as well as extrahepatic pathologies such as renal fibrosis (e.g., Sanderson, N. et al., Proc. Natl. Acad. Sci. USA 92:2572-2576 (1995)).
TGF-β1 and its receptors are overexpressed in injured blood vessels and in fibroproliferative vascular lesions leading to overproduction of extracellular matrix (e.g., Saltis, J. et al., Clin. Exp. Pharmacol. Physiol. 23: 193-200 (1996); McCaffrey, T. A. et al., J. Clin. Invest. 96: 2667-2675 (1995)).
Anti-TGF-β antibodies reduce scar formation and improve the cytoarchitecture of the neodermis in rats (e.g., Shah, M., J. Cell. Sci. 108: 985-1002 (1995)), improve healing of corneal wounds in rabbits (e.g., Moller-Pedersen, T., Curr. Eye Res. 17:736-747 (1998)), and accelerate wound healing of gastric ulcers in rats (e.g., Ernst, H., Gut 39: 172-175 (1996)).
Radiation fibrosis is a frequent sequel of therapeutic or accidental radiation overexposure in normal human tissues. TGF-β1 plays a central role in the initiation, development, and persistence of radiation fibrosis, as has been reviewed recently (e.g., Martin, M. et al., Int. J. Radiat. Oncol. Biol. Phys. 47:277-290 (2000)).
Organ transplantation is complicated in many instances by chronic rejection and for some organs such as the kidney, it is the major forms of graft loss. In human patients, chronic rejection of lung and kidney transplants is associated with increased expression of TGF-β within the tissue (e.g., El-Gamel, A. et al., Eur. J. Cardiothorac. Surg. 13: 424-430 (1998); Shihab, F. S. et al., J. Am. Soc. Nephrol. 6:286-294 (1995)).
TGF-β is implicated in peritoneal adhesions (e.g., Saed, G. M. et al., Wound Repair Regeneration 7: 504-510 (1999)). The peritoneal and sub-dermal fibrotic adhesions could be prevented by inhibitors of ALK5 and/or ALK4.
The tumor cells and the stromal cells within the tumors in late stages of various cancers generally overexpress TGF-β. This leads to stimulation of angiogenesis and cell motility, suppression of the immune system, and increased interaction of tumor cells with the extracellular matrix (e.g., Hojo, M. et al., Nature 397: 530-534 (1999)). Consequently, the tumor cells become more invasive and metastasize to distant organs (e.g., Maehara, Y. et al., J. Clin. Oncol. 17: 607-14 (1999); Picon, A. et al., Cancer Epidemiol. Biomarkers Prev. 7:497-504 (1998)).
Plasminogen activator inhibitor-1 (PAI-1) is the major physiological inhibitor of both tissue-type plasminogen activator and urokinase-type plasminogen activator. Elevated levels of PAI-1 are associated with thrombosis and vascular disease, suggesting that high plasma PAI-1 may promote a hypercoagulable state by disrupting the natural balance between fibrinolysis and coagulation (e.g., Vaughan, D. E., J. Invest. Med. 46: 370-376 (1998)). It is known that TGF-β stimulates the expression of PAI-1 (e.g., Dennler, S. et al., EMBO J. 17: 3091-3100 (1998)). Accordingly, inhibition of the production of PAI-1 with an inhibitor of the TGF-β signaling pathway could produce a novel fibrinolytic therapy.
Activin signaling and overexpression of activin is linked to pathological disorders that involve extracellular matrix accumulation and fibrosis (e.g., Matsuse, T. et al., Am. J. Respir. Cell Mol. Biol. 13:17-24 (1995); Inoue, S. et al., Biochem. Biophys. Res. Comm. 205:441-448 (1994); Matsuse, T. et al., Am. J. Pathol. 148:707-713 (1996); De Bleser et al., Hepatology 26:905-912 (1997); Pawlowski, J. E., et al., J. Clin. Invest. 100:639-648 (1997); Sugiyama, M. et al., Gastroenterology 114:550-558 (1998); Munz, B. et al., EMBO J. 18:5205-5215 (1999)), inflammatory responses (e.g., Rosendahl, A. et al., Am. J. Respir. Cell Mol. Biol. 25:60-68 (2001); cachexia or wasting (Matzuk, M. M. et al., Proc. Natl. Acd. Sci. USA 91:8817-8821 (1994); Coerver, K. A. et al., Mol. Endocrinol. 10:534-543 (1996); Cipriano, S. C. et al., Endocrinology 141:2319-2327 (2000)), diseases or pathological responses in the central nervous system (e.g., Logan, A. et al., Eur. J. Neurosci. 11:2367-2374 (1999); Logan, A. et al., Exp. Neurol. 159:504-510 (1999); Masliah, E. et al., Neurochem. Int. 39:393-400 (2001); De Groot, C. J. A. et al., J. Neuropathol. Exp. Neurol. 58:174-187 (1999); John, G. R. et al., Nat. Med. 8:1115-1121 (2002)) and hypertension (e.g., Dahly, A. J. et al., Am. J. Physiol. Regul. Integr. Comp. Physiol. 283: R757-767 (2002)). Studies have shown that TGF-β and activin can act synergistically to induce extracellular matrix production (e.g., Sugiyama, M. et al., Gastroenterology 114; 550-558 (1998)).
WO 00/61576 and US 2003/0149277 A1 disclose triarylimidazole derivatives and their use as ALK5 inhibitors. WO 01/62756 A1 discloses pyridinylimidazole derivatives and their use as ALK5 inhibitors. WO 02/055077 A1 discloses use of imidazolyl cyclic acetal derivatives as ALK5 inhibitors. And, also, WO 03/087304 A2 discloses tri-substituted heteroaryls and their use as ALK5 and/or ALK4 inhibitors.